Laser guidance is a technique of guiding a weapon such as a missile or a bomb to a target using a laser beam or spot. As known in the art, there are both internal laser designators and external laser designators. A laser guided weapon (LGW) is weapon which uses a seeker (e.g., targeting sensor) to detect laser energy reflected from a laser marked/designated target and through signal processing provides guidance commands to a control system which guides the LGW to the target point from which the laser energy is being reflected.
An example of an external designator is a beam rider. In beam riding, first, an aiming station in the launching area directs a narrow radar or more commonly a laser beam at a target, such as an enemy aircraft or tank. Then, the LGW (e.g., missile or other projectile) is launched and at some point after launch is “gathered” by the radar or laser beam when it flies into it. From this stage onwards, the LGW attempts to keep itself within the beam, while the designator station keeps the beam pointed at the target. The LGW, controlled by a laser or radar seeking guidance kit including photodetectors and a computer inside it, “rides” the beam to the target.
More commonly, the guidance system is internal to the LGW and operation is similar to semi-active radar homing. With this technique, the laser is kept pointed at the target and the laser beam bounces off the target and is scattered in all directions, known as “painting the target”. The LGW is launched or dropped near the target. When the LGW is close enough that some of the reflected laser energy from the target reaches it, a laser seeker detects which direction this energy is coming from and adjusts the LGW trajectory towards the source/target. As long as the LGW is in the general area and the laser is kept aimed at the target, the LGW is generally guided accurately to the target.
Many existing LGWs or guidance kits utilize weather vane detection sensors as key elements in the vehicle control loop. As a result, steering of the LGW defaults to classic Velocity Pursuit Guidance (VPG). VPG is a guidance technique that points the guidance beam on the target during which the flight direction (velocity vector) of the LGW is commanded towards the current target location. Against stationary targets this provides satisfactory terminal engagement performance, usually corrupted only by residual vertical bias uncertainties and common mode instrumentation and seeker errors. Against moving targets, however, VPG generally defaults to a tail chase endgame regardless of the initial engagement geometry. In this environment, sluggish g-limited airframes typically run out of maneuver space before their speed advantage can overtake the target and they shortfall their intended impact points by an amount dependent on the engagement geometry, LGW airframe capability, terminal lasing time, and target speed. This terminal guidance effect renders these particular LGWs being ineffective against all but the slowest moving targets.
Laser lead guidance is known for both internal laser designators and external laser designators, including guidance for compensating for shortfall due to target movement. In laser lead guidance the guidance beam is pointed on the target. For example, compensation for shortfall has been addressed by replacing the LGW steering implementation with Proportional Navigation Guidance (PNG) and mitigating moving target shortfall by building lead into the LGW control loops through detection sensor inertial stabilization. Problems with the PNG approach for solving the above-described shortfall problem include generally being costly for existing LGWs because of the need to replace the sensors and implement PNG for every LGW.